Electric Nightmares (glowplug/relays/fuses)

Hey Everybody,

Trying to make sense of the electrics in my new old Landrover. It’s a Series 2a with a 300tdi conversion. It has a push start and a sprung ignition. Almost everything is routed through relays (lights, indicators, full beams, wipers). Anyone know why that would be?

All the fuses are continental 16amp currently, I thought they were supposed to be 30ish? The plastic casing to the fuse for the headlights regularly melts but the fuse doesn’t blow - any ideas?

The only thing that isn’t on a relay is the glow plugs. It’s reluctant to start when temp gets below 10c and the glow plug light is always on (until the engine starts) so figured there’s an issue. Replaced the plugs and two were sooted, other two were oily. No blue smoke and recently had a rocker leak so not overly worried about that.

Went to test the current - first time using a multi meter but the first plug is seemingly only getting 1volt, amperage is 0.4 at 200ma setting. Does this indicate a short/bad earth or am I missing something?

A lot there - apologies but figured they might all be connected in some way.

Any help would be fab.

Sprung ignition?
If it's supposed to be a 30A fuse but only 16A then that's probably why it's getting hot.
Do the math and see what you get

Your [rough] location? Trying to work out issues on what is a non standard truck is difficult.
Routing through relays is the modern way. In cars today with all the functions if all worked direct then loom would likely be twice the weight [ bigger cables to carry current] I think we have to work on the assumption system has been changed to a later type 300 glow system with a glow relay.
With a good battery 300's will start with no glow. Small fuse may be limiting flow to activate relay correctly.

kermit_rr said:

Sprung ignition?
If it's supposed to be a 30A fuse but only 16A then that's probably why it's getting hot.
Do the math and see what you get

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Ah yes, ‘sprung’ is just a term I’ve made up. Ignition - first position to the right gives power to most things and readies the push start, the next position is a sort of spring that I’ve deduced is for heating the glow plugs.

tottot said:

Your [rough] location? Trying to work out issues on what is a non standard truck is difficult.
Routing through relays is the modern way. In cars today with all the functions if all worked direct then loom would likely be twice the weight [ bigger cables to carry current] I think we have to work on the assumption system has been changed to a later type 300 glow system with a glow relay.
With a good battery 300's will start with no glow. Small fuse may be limiting flow to activate relay correctly.

Click to expand...

Thanks toto, yes it’s a real casserole. Have both Haynes but working out which bits are what is tricky.

I’m in Berkshire

I can’t find a glow relay anywhere, seems like the plugs are wired straight to the ignition (hence the sprung position 2). When I hold the key in that position the power to the plugs definitely increases but to the levels I mentioned previous.

Relays means you can use thinner wire and light duty switches on the control side.

No need for multimeter to test glow plugs, just test them across a battery, use pliers to hold them, see youtube if unsure.

S2 had a single 30 amp glass fuse, I think 2A went to two glass fuses, if you have multiple fuses then it would be safe to assume each fuse is for one item, ie wipers.

JRo said:

Ah yes, ‘sprung’ is just a term I’ve made up. Ignition - first position to the right gives power to most things and readies the push start, the next position is a sort of spring that I’ve deduced is for heating the glow plugs.

Click to expand...

Sounds like standard 2a ignition switch.

lynall said:

Relays means you can use thinner wire and light duty switches on the control side.

No need for multimeter to test glow plugs, just test them across a battery, use pliers to hold them, see youtube if unsure.

S2 had a single 30 amp glass fuse, I think 2A went to two glass fuses, if you have multiple fuses then it would be safe to assume each fuse is for one item, ie wipers.

Click to expand...

Thanks Lynall, you’re right about the fuses being separate, would that mean that lower amp fuses are ok or should they still be 35s?

Makes sense about the relays.

Done the jump lead test, plugs are fine so assuming an electrical issue somewhere. As I say no glow plug relay so wondered what would let some power through but seemingly not enough.

JRo said:

Thanks Lynall, you’re right about the fuses being separate, would that mean that lower amp fuses are ok or should they still be 35s?

Makes sense about the relays.

Done the jump lead test, plugs are fine so assuming an electrical issue somewhere. As I say no glow plug relay so wondered what would let some power through but seemingly not enough.

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A simple heavy duty switch will do what you need, what ignition switch do you currently have? I ask as some can handle the current draw of the glow plugs, so it could just need a simple wiring change.

16 amp is a bit heavy for most circuits, if you look at the original s2/2a wiring diagram you will see that only some things were protected by the fuse (horn and wipers spring to mind) most circuits (what there was) were I think unfused.
As an example next time you see a hgv in the dark, every side light down one side and half he front side lights and half the rear side lights uses one single 10 amp fuse, yes they are nearly all led (0.5 watt each) now, but even when they were bulbs it was still one single 10 amp fuse.

lynall said:

A simple heavy duty switch will do what you need, what ignition switch do you currently have? I ask as some can handle the current draw of the glow plugs, so it could just need a simple wiring change.

16 amp is a bit heavy for most circuits, if you look at the original s2/2a wiring diagram you will see that only some things were protected by the fuse (horn and wipers spring to mind) most circuits (what there was) were I think unfused.
As an example next time you see a hgv in the dark, every side light down one side and half he front side lights and half the rear side lights uses one single 10 amp fuse, yes they are nearly all led (0.5 watt each) now, but even when they were bulbs it was still one single 10 amp fuse.

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Ah brilliant, I’m away for a few days now but will check when I’m home and report back.

Interesting about the fuses. So if anything mine are overkill. Any idea what would make a plastic continental fuse case melt without blowing the fuse? It’s only the headlight fuse. I’ve just been replacing them so far but I’m getting through them like skittles.

JRo said:

Ah brilliant, I’m away for a few days now but will check when I’m home and report back.

Interesting about the fuses. So if anything mine are overkill. Any idea what would make a plastic continental fuse case melt without blowing the fuse? It’s only the headlight fuse. I’ve just been replacing them so far but I’m getting through them like skittles.

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Probably right on the limit of what the fuse can handle, so a dead short would blow the fuse, but running it at 99 percent could melt the casing.
Wiring could be to small a section/corroded connectors/uprated bulbs/damaged wiring/poor earth.

Are you sure it's an electrical problem with regards to poor starting maybe it's more fuel related?
Son's 200tdi starts first flick of the key at recent temperature without glow plugs.

lynall said:

Probably right on the limit of what the fuse can handle, so a dead short would blow the fuse, but running it at 99 percent could melt the casing.
Wiring could be too small a section/corroded connectors/uprated bulbs/damaged wiring/poor earth.

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Brilliant, thanks for all the input Lynall. I’ll get into it and report back.

Anaconda said:

Are you sure it's an electrical problem with regards to poor starting maybe it's more fuel related?
Son's 200tdi starts first flick of the key at recent temperature without glow plugs.

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To be honest, I’m not sure what it is. Plugs are a hunch that I might be stretching too thin. Pretty sure they aren’t working properly anyway. What could the fuel issue be?

JRo said:

To be honest, I’m not sure what it is. Plugs are a hunch that I might be stretching too thin. Pretty sure they aren’t working properly anyway. What could the fuel issue be?

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Probably worth noting that once it’s started once, it’s fine for the rest of the day (depending on how cold it is)

JRo said:

To be honest, I’m not sure what it is. Plugs are a hunch that I might be stretching too thin. Pretty sure they aren’t working properly anyway. What could the fuel issue be?

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Fuel could be an air leak somewhere in the fuel system maybe.

Check if it has a Ballast Resistor. Original 2A if Diesel would have had one, the TDi would not.
The Ballast Resistor would reduce the voltage to plugs if still wired that way.
It seems strange that most circuits have an excess of fuses and relays yet probably the highest draw does not.
You do need to make sure the plugs turn off on some sort of timer or resistance switch or they will soon burn out.

Hi all, sorry to leave you hanging it's been a loooong month. Finally got the chance to get into it this week. I've sorted the glow plug issue, as @Shedload suggested it was run through the ballast. Have now wired it straight through to ignition and cleaned up the connectors. It now starts first turn and with less rattle. Pretty sure it's masking another problem though and probably is fuel related, Anaconda. Will move onto stop solenoid and lift pump today and see what's what.

I've replaced the wiring on the headlight fuse and so far, so dim.

Appreciate all the input!